The recently developed cellulose nanofibers are plant-derived native nanofillers, and have attracted interest as a low-specific-gravity and high-strength composite material for resins (see PTL 1).
However, at the current level of technology, cellulose, with large numbers of hydroxyl groups, needs to be defibrated in water in order to be reduced to nano-level sizes. In order to use such water-defibrated cellulose nanofibers as a composite with various resins, it is necessary to subject the product cellulose nanofibers to dehydration and solvent displacement. Further, because of its propensity to form intermolecular hydrogen bonds, cellulose tends to reaggregate during a cellulose nanofiber dehydration process, and becomes poorly dispersed in resin.
As a solution to these problems, a technique is reported that produces cellulose nanofibers by refining cellulose in an organic solvent, instead of in water (see PTL 2). Though this technique is alleged to reduce the drying cost by not using water, combining the cellulose nanofibers with resin requires dispersing cellulose in an organic solvent, and removing the organic solvent after the cellulose is reduced to nano fibrils. The technique thus still involves complicated procedures for nanofiber production.
In other words, there is a need to establish a technique with which cellulose nanofibers can be combined with various resins at lower costs and with simpler procedures.
Techniques are reported that produce cellulose nanofibers by refining cellulose in resin, without using a solvent (see PTL 3, and PTL 4) . These techniques greatly reduce the difficulties in combining cellulose nanofibers with resin. The polyester resins used in PTL 3, and the acrylic resins used in PTL 4 need to be used in large amounts to refine cellulose. Because these polyester and acrylic resins are used in large amounts, the resins are not reactive in curing of a resin having a reactive double-bond group. These resins thus remain as uncured material in a molded body, and act as a plasticizer to deteriorate the quality of the molded body. Because low moisture absorption is typically desired for a molded body of a compound having a reactive double-bond group, a compound having a reactive double-bond group and a hydroxyl value of 10 KOHmg/g or less is used as a monomer. However, the methods of PTL 3 and PTL 4 cannot refine cellulose with a compound having a reactive double-bond group and a hydroxyl value of 10 KOHmg/g or less.